The present invention generally relates to methods and apparatus for measuring contaminant mobile ions in dielectric materials. More particularly, the present invention relates to methods and apparatus for measuring contaminant mobile ions in a dielectric portion of a semiconductor.
Generally, semiconductor devices are formed by patterning substantially coplanar conductive traces or interconnects onto the surfaces of substrates followed by layering of the substrates. The substrates are typically formed of dielectric materials or include portions of dielectric material (e.g., dielectric layers or films). The portions of dielectric material (i.e., dielectric portions) are included on the substrates to electrically separate interconnects of each of the layered substrates and exemplary dielectric materials used for semiconductor devices include, but are not limited to, silicon dioxide (oxide) and silicon nitride.
Due to processing of the substrates and other conditions, the dielectric portions often contain variable levels of electrically charged contaminant mobile ions. Such electrically charged ions within the dielectric portions can reduce reliability of semiconductor devices such as metal oxide semiconductor (MOS) devices. As an example, ionized alkali metal atoms (e.g., Na+ and K+) are mobile in oxide layers, and move through gate oxides of MOS devices under the influence of the electric fields generated between gate electrodes and substrates during MOS operation. Over time, mobile ions in gate oxides can drift toward interfaces between the gate oxides and underlying substrates and the resulting changes in MOS device threshold voltage levels may become significant enough to cause electrical performance degradation in circuits that incorporate the MOS device.
To assist in maintaining low levels of mobile ion contamination, it is desirable to measure the contamination of mobile ions. Capacitance/Voltage (c/v) methods, bias temperature treatment methods and other similar methods are commonly employed to monitor such contamination by inducing drift or mobilization of mobile ions within the dielectric materials and measuring differences in electric potential or voltage caused by the mobile ions. Examples of such methods are discussed in commonly owned U.S. Pat. No. 5,963,783, issued to Lowell et al on Oct. 5, 1999, which is herein fully incorporated by reference. These methods commonly employed to measure contamination can be improved as the differences in electric potential upon which these commonly employed contamination measurements may be based can be at least partially caused by non-contaminant mobilized ions or charges. Additionally, contaminant mobile ions may remain immobilized during contamination measurements such that differences in electric potential are unrepresentative of actual contamination levels.
In view of the foregoing, it is desirable to provide methods and apparatus for measuring contaminant mobile ions in dielectric materials. In addition, it is desirable to provide methods and apparatus for measuring contaminant mobile ions in a dielectric portion of a semiconductor. Furthermore, additional desirable features will become apparent to one of ordinary skill in the art from the drawings, foregoing background of the invention and following detailed description of the drawings, and appended claims.
In accordance with the present invention, methods and apparatus are provided for measuring contaminant mobile ions in a dielectric portion of a semiconductor. The apparatus comprises a heat source that is configured to elevate a temperature of the dielectric portion of the semiconductor and mobilize the contaminant mobile ions. The apparatus is also comprised of a fluid source that is configured to expose the dielectric portion of the semiconductor to a mobilizing fluid having contaminant ion releasing atoms that further assists in mobilizing the contaminant mobile ions. The apparatus further comprises a mobile ion measurement unit configured to perform measurements of the contaminant mobile ions in the dielectric portion of the semiconductor after the temperature of the dielectric portion of the semiconductor is elevated and the dielectric portion of the semiconductor is exposed to the mobilizing fluid.